version 2.0 rev 18 Feb 2021
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2.6.3.5 Global Shutter External Exposure Triggering (Overlap Mode)
In overlap mode, every positive edge of an External trigger will trigger a signal frame read out and start a new
exposure.TheperiodofExternaltriggerpulsedenesboththeexposuretimeandcycletime.Notethatwhen
anacquisitionstarts,therstpositiveedgeofthetriggerwillinitiatetherstexposurebutalsooutputaframe
that has an incorrect exposure which is therefore discarded. The next positive edge of the trigger will end
therstexposureandstartanewframereadout.Fromthegurebelow,itiscanbeseenthattheminimum
exposuretimeisapproximatelytwoframereadoutperiods.Therstreadoutperiodisusedtoreadoutthe
“Signal” frame while the second is used to read out the “Reference” frame for the subsequent “Signal” frame.
If the period of the external trigger is less than the minimum period discussed above any positive edge occurring
during the “Signal” and “Reference” frames will be ignored. The ARM signal indicates when positive going edges
will be accepted.
Figure 32: Global Shutter External Exposure Triggering (Overlap Mode)
Table 29: Global Shutter External Exposure (Overlap Mode) Timing Parameters
Parameter Minimum Maximum
Exposure (EXT Trig Period) 2 Frames + 2 InterFrames 30 s
Cycle Time ( EXT Trig Period) 2 Frames + 2 InterFrames 30 s
External Start Delay (1st Frame Only) 0 1 Row + Charge Transfer Time
External Start Delay (Frame #2... Frame #n) Charge Transfer Time Charge Transfer Time
EXT Trig Pulse Width 2 Sensor Speed Clock Cycles -
NOTE: In global shutter external exposure mode, taking exposures in darkness of 270 ms or more will lead
to increased noise. A reference frame is taken at the start of the exposure and the camera then idles until
the end is signalled, which triggers the image readout. The increased noise is coming from the separation
of the reference frame and the image frame. This is less prominent with deeper cooling.
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